The full picture, not just the monthly number: price, tax, down payment and trade-in in, monthly payment, total interest, and true total cost out.
The loan amount is the price plus sales tax, minus down payment and trade-in value. The monthly payment then follows the standard amortization formula. Watching total interest matters: stretching a loan from 48 to 72 months drops the payment but can add thousands in interest.
Why include sales tax in the loan? Most buyers pay tax on the vehicle price at purchase and roll it into the loan. Some states credit the trade-in against the tax — if yours does, lower the tax rate to match.
What APR should I enter? The rate on the actual loan offer. A one-point APR difference on a $30,000, 60-month loan is roughly $800 of interest.